1. Field of the Invention
The present invention relates to a magnetic bubble device driver. More particularly, the invention relates to a driver for magnetic bubble devices.
Magnetic bubble device drivers known in the art supply two out-of-phase sine wave currents to the X-type and Y-type orthogonal coils positioned in operative proximity with a magnetic bubble chip, so that an induced rotating magnetic field will trace a circular locus and magnetic bubbles in the chip will be transferred. Since the circular locus induced by sine wave currents provides a constant speed of rotation, good behavior is expected from the magnetic bubbles. However, when the magnetic bubbles are used in a memory system, it is necessary to start and stop the rotating magnetic field and to reverse the direction thereof so that access time may be reduced and/or power consumption of the driver may be reduced. To accomplish such control of the magnetic field, the sine wave generator requires very complicated control.
The present invention relates to a device which utilizes the cylindrical magnetic domain or magnetic bubble produced when a bias magnetic field is applied to single crystal of orthoferrite or garnet grown on a thin sheet, or to an amorphous magnetic thin sheet or other magnetic thin sheet which provides uniaxial magnetic anisotropy. This is the magnetic bubble chip of a magnetic bubble device. More particularly, the invention relates to a driver for a magnetic bubble device utilizing magnetic bubbles. The driver of the invention provides a rotating magnetic field substantially parallel to the surface of the magnetic bubble chip.
2. Description of the Prior Art
A cylindrical magnetic domain or magnetic bubble is produced when a bias magnetic field is applied in an easy magnetization direction normal to the plane of the sheet of orthoferrite, garnet or other uniaxial magnetic anisotropic single crystal. The sheet is thin and has a magnetizable axis normal to the plane of the sheet. The sheet may be grown. The bias magnetic field may be applied to the plane of a uniaxial magnetically anisotropic armophous magnetic film whose easy magnetization axis is normal to the plane thereof. The magnetic bubble so produced may be moved, transported or transferred by producing a gradient of the magnetic field normal to the plane of the sheet. This effect is described in detail in a textbook entitled, "Domain Behavior in Some Transparent Magnetic Oxides", by Remeika and H. J. Williams, et al., Journal of Applied Physics, 1959, Vol. 30, pages 215 to 225, and in a textbook entitled, "Properties and Device Application of Magnetic Domain in Orthoferrites" by A. H. Bobeck, Bell System Technical Journal, Vol. 46, pages 1901 to 1925.
Logic, operator, memory, or other devices, applicable to digital data processing may utilize magnetic bubbles. Such devices provide correspondence between the presence and absence of the magnetic bubble to binary information. The devices combine various control functions, such as generation, transfer, sensing, elimination and splitting of the magnetic bubbles.
There have been many proposals for controlling magnetic bubbles. The most popular one is that disclosed by U.S. Pat. Nos. 3,534,347 and 3,543,252, by which various Permalloy patterns formed on a magnetic bubble chip are controlled by a rotating magnetic field parallel to the plane of the magnetic bubble chip. According to this method, Permalloy patterns such as, for example, T-shaped and I-shaped patterns formed on a magnetic bubble chip are externally driven by a rotating magnetic field extending parallel to the plane of the magnetic bubble chip so that magnetic bubbles may be attracted by magnetic poles produced on the Permalloy patterns. The rotating magnetic field thereof is induced by two out-of-phase sine wave currents supplied to two substantially perpendicularly positioned solenoid coils. A magnetic bubble produced inside the coils is controlled by a rotating magnetic field of circular locus.
The circular locus of the rotary magnetic field is favorable due to a uniform speed of rotation thereof. However, the circular locus induced by sine wave currents is disadvantageous for the desired application. It is very likely that start or stop or reverse rotation control of the rotating magnetic field, so that access time may be reduced or power consumption of the system may be decreased, creates problems. The start, stop or reverse control of the rotating magnetic field by sine wave currents becomes very complicated when the transient response of the circuit is considered.
In another proposal, a capacitor is connected in parallel with each of the coils which produce the rotating magnetic field, so that resonance of the coil and capacitor may vary the supplied square wave control current to sine wave current. However, this proposal also requires a complicated set of operating conditions such as, for example, the timing of a square wave control current or the duration thereof.
The start, stop or reverse control of the rotating magnetic field may be simplified by supplying two out-of-phase square wave currents to the coils, so that the locus of the rotating magnetic field may form a square. However, the speed of rotation of the magnetic field formed by square wave currents is not uniform, but varies in a step-like manner. This effect is not favorable for controlling a magnetic bubble, because a sudden change in speed of the locus is equivalent to a highspeed magnetization of the Permalloy pattern and the magnetic bubble. Considering the mobility of the domain wall of the magnetic bubble chip and the characteristics of the Permalloy pattern, the sudden change in speed of the locus lowers the operation margin of the system.
The principal object of the invention is to provide a magnetic bubble device driver which very easily and simply controls start, stop and reverse of the magnetic field.
An object of the invention is to provide a magnetic bubble device driver which produces a magnetic field which rotates at a uniform constant speed, which driver has a margin of operation free from deterioration.
Another object of the invention is to provide a magnetic bubble device driver comprising a very simple circuit.
Still another object of the invention is to provide a magnetic bubble device driver of simple structure, which is inexpensive in manufacture and functions efficiently, effectively and reliably to produce a magnetic field which rotates at a uniform constant speed and has a linearly varying locus.
Yet another object of the invention is to provide a magnetic bubble device driver having reduced power consumption of the drive coils.